Office was supposed to be Windows 8's killer app, but it works poorly on touch PCs. Instead, the new killer app could be iTunes

PC sales are plunging, down 10.1 percent this year and more than 15 percent among consumer purchases. Windows 8.1 doesn't fix Windows 8's inherently unusable experience. Anyone who wants a new PC is stuck, faced with switching to a Mac, finding a Windows 7 PC, or waiting a few years in hope that Microsoft will eventually snap out from its Windows 8 delusion.

Microsoft Office was supposed to be Microsoft's trump card for Windows 8, providing an essential business tool unavailable on iPads and Android tablets, and in a better version than the one offered for OS X. But it works poorly on touch devices, especially the crop of Windows 8 tablets that Microsoft has been selling so ineffectually in its TV ads. Office matters to enterprises, but they're adopting Windows 7.

Ironically, Windows 8's Metro UI and the marketing around it are focused on edutainment apps, not the business crowd. Home users who need Office already have it on Windows XP or 7 PCs that will likely run just fine for years to come. Edutainment -- games, media players, social networking, and so on -- is Microsoft's best hope to get people to pay for a Windows 8 PC.

But Windows 8's Metro media player duo -- Xbox Music and Xbox Videos -- falls short. It's focused on getting users to buy or rent media from the Microsoft Store, hiding users' existing media content, such as their ripped CDs and DVDs. It also isn't designed to stream media to or from tablets or to stereos, TVs, and speakers. Thus, it's not a great entertainment center.

There's an entertainment center for Windows that does all those things, though: Apple's iTunes. But it's a Windows 7 app, so it runs in the legacy Desktop part of Windows 8 that's hard to use in a touch or tablet environment, as I discovered when I recently compared media tablets.

What if Apple made a Metro version of iTunes, similar to the iOS version that works quite well on an iPad, but with the ability to import local media and create ringtones that desktop iTunes also has? That would turn Windows 8 into an entertainment powerhouse, with full, flexible support for music, movies, TV shows, podcasts, e-books (which Metro can't do outside of Kindle books) and perhaps even photo albums across both PCs (Windows and OS X) and Apple mobile devices, including the Apple TV, which remains the best media-streaming box out there.

Suddenly, there'd be something really useful -- and important -- to be done in Windows 8's Metro environment, which is supposedly the future core of Windows. If Microsoft ever made a good Office app for Metro (no sure bet), then Windows 8 might get a second look in business, as well as for home-business users. An iTunes/Office duo in Metro would be killer.

Of course, Apple has no strong reason to make a Metro version of iTunes, any more than it has to make a version for Android. When it first made iTunes available for Windows in 2003, that cemented iTunes's status as the media center. Back then Apple had no mobile devices (the iPod was a mere two years old) and Macs were just coming back from death's door.

Today, Apple is a cash machine, with strongly profitable mobile and Mac businesses. It already has most Windows users, and it knows that withholding iTunes from Metro won't reduce its user base. Instead, WinXP and Win7 users will stay where they are, get Macs, or -- most likely -- shift to iPads for media consumption, giving Apple both hardware and media revenues.

Yes, if Windows 8 PCs were to resurge, boosted by a Metro iTunes version, Apple would net more media revenues but at the potential cost of lower hardware revenues, which still dwarf iTunes revenues. Perhaps one day that calculation will change. PC users can only hope.

InfoWorld executive editor Galen Gruman analyzes the latest issues in mobile technology and the consumerization of IT. He has also written or co-written more than 40 how-to books, on iOS, iPad, Windows 8, OS X, and desktop publishing.